A common method used to separate analytes within a sample is liquid chromatography. Liquid chromatography employs specific chromatographic columns and one or more mobile phases which are used to both equilibrate the column and elute analytes therefrom. Chromatography columns are used to effectuate the separation, purification and study of analytes contained within a homogeneous or heterogeneous sample. Columns are packed with sorbent material (also referred to as the “stationary phase”) that provides a chemical milieu with which analytes of a sample can interact. Generally, the sorbent material contains a functional group having a specific chemistry. For example, reverse-phase columns have a stationary phase comprising molecules with one or more hydrophobic groups. These hydrophobic groups, e.g., a C18 hydrocarbon chain, will interact with other molecules via hydrophobic interaction. This hydrophobic interaction can be interrupted using an organic mobile phase, thus eluting various analytes from the stationary phase.
The most commonly used chromatographic columns, referred to herein as “conventional columns”, are comprised of a column tube into which sorbent is packed, and inlet and outlet end fittings, which facilitate connection to the fluid stream, and which also contain filters that are designed to keep the sorbent bed within the column tube itself. These filters are disposed at each end face of the column tube.
Liquid chromatography columns can range in size depending upon the desirable application including small capillary columns. Capillary columns are particularly advantageous when relatively small sample sizes (referring to concentration) are examined. Another advantage observed with the use of capillary columns is their small connections to other columns or instruments thereby effectuating minimum loss of sample and gaining greater efficiency of chromatographic separation.
To effectuate concentrating a sample, retaining frits have been developed for chromatographic use. To date, however, most retaining frits are in a cartridge type format. Since their small dimensions make them difficult to use with relatively large dead volumes that lead to undesirable peak dispersion.
Thus, it is desirable to have retaining frits for capillary use that have a relatively large inner diameter in order to maximize the surface area of the stationary phase while at the same time their fluidic connections are smaller than their diameter. Moreover, it is desirable to have a retaining frit disposed within a capillary column thereby minimizing fluid transfer dynamics and effectuating separation efficiency.